This invention relates to an apparatus for holding paper in a paper copier having a duplexing capability (duplex copiers).
Considerations of the cost of paper and convenience of handling make duplex copying desirable. It is also desirable that the inclusion of a duplex feature in a copying machine results in little or no increase in the operations performed by the machine operator or reduction in the speed of copying. Copending U.S. application, Ser. No. 192,269, filed on the same day as this application and assigned to a common assignee, discloses a simple, reliable, and effective duplex printing apparatus for use with high speed laser printers as well as paper copiers. The duplex printing apparatus of the referenced application can be used with a paper copier having two separate paper feeding stations similar to the paper feeding stations of the referenced application. These paper feeding stations include a cassette which stores a plurality of sheets of paper in a stack for automatic delivery into the copier by a paper feeding means. Blank sheets of paper are fed from a first cassette to receive an image on one side of an original. The sheets are then delivered to the second cassette by the duplex printing apparatus where they are disposed to be fed back into the copier to receive an image of a second original on the remaining blank side.
Cassettes used in copiers such as those disclosed in U.S. Pat. No. 3,972,612, which is hereby incorporated by reference as if specifically set forth herein, comprise: a container which encloses a chamber; an intermediate support plate within the container which is biased toward the top of the container by a spring or springs disposed between the intermediate support plate and the bottom of the container; and guide and separation means attached to the container for aligning and confining a stack of paper sheets resting on the intermediate support plate within the container. The guide and separation means usually include upright sections which align the front, sides and back edges of the stack of paper, and an extended section which extends across a portion of the top sheet of paper in the stack and against which the springs below the intermediate support plate push or bias the stack. When it is desired to feed a single sheet of paper into the copier, a portion of a rotating roller is caused to come in contact with the top sheet forcing the front edge of the sheet to move against the front upright sections of the guide and separation means. As the movement continues, the paper begins to buckle until the front edge of the paper slips up over the front upright sections. The top extended sections of the guide and separation means along with the biasing action of the spring ensures that the top sheet is very close to the top of the front upright sections but not above them. The above operation causes only the top sheet of the stack to be separated from the stack for feeding.
A typical mode of duplex copying requires that a plurality of copies of a first original is made and the copies stored. Then a second original is placed in the copier and the copies of the first original are fed back into the machine to receive images of the second original on the remaining blank sides of each of the copies. Special provisions and operating procedures are required in the prior art to accomplish plural duplex copying in this manner. For example, in U.S. Pat. No. 3,972,612, a paper feeding cassette receives simplex copies but is positioned at a discharge station on the machine. The simplex copies accumulate on the internal support plate of the cassette with the front edge of the copies resting above the extended sections of the guide and separating means. The cassette must be removed from the discharge station, the front edges of the simplex copies pressed manually below the top extended sections of the guide and alignment means, and the cassette mounted at a paper feeding station. Alternatively, the internal support plate can be locked in a load position against the action of the biasing spring allowing the single copies to fall below the top extended section of the guide and separating means. Then, when the cassette is repositioned at the paper feed station, the internal support plate must be manually unlocked.
In U.S. Pat. No. 4,017,181, a cassette is disclosed which contains two paper holding chambers. A lower chamber feeds fresh sheets of paper for simplex printing. These sheets are discharged onto a tray and then manually delivered to an upper chamber of the same cassette and the upper chamber is then manually positioned in the cassette to feed the simplex copies back into the machine for duplex copying without removing the cassette.
In each of the above patents, manual operations and attention by the operator are required to provide for duplex printing thereby slowing down the duplex printing operation.
In U.S. Pat. No. 3,645,615, a duplex copying machine is disclosed in which a movable sheet guide is repositioned to guide simplexed copy sheets into a tray forming a portion of a second feeding station. The second feeding station automatically stacks and refeeds the simplexed copy sheets back into the copier for duplexing. If only simplexed copies are required, the movable sheet guide is placed in a position to discharge the simplexed copy sheets into a discharge tray.
In the above patent, to refeed sheets from the feeding station, feed rollers are lowered onto the stack of paper in the tray to contact the top sheet. Various retaining means are provided with the tray to align the edges of the stack on the tray including a front retaining member 70 which includes a top tab 78 that rests on the top sheet of the stack. However, when sheets are first loaded into the second feeding station for duplexing they are positioned on the top of the tab 78. The retaining member 70 with tab 78 must be moved to allow the tab 78 to come to rest on the top sheet of the stack. Then, the feed roller rotates in a first direction to remove the edge of the top sheet from under the tab 78 and then reverses direction to move the top sheet over the tab 78 into the copier. Hence, the action of the duplexing station, although automatic, is quite different and more complicated that the approach described previously in connection with U.S. Pat. Nos. 3,972,612 and 4,017,181.